Simple and easy: make a cat themed ATC, send it to your partner. Any kind of cat will do, real or not. Senders choice, so you can make your ATC before partners are assigned. ALL ATCs are 2.5"x3.5" in size. No exceptions!

No rating requirement for this swap, but that does not mean that I'm not going to remove questionable swappers before partners are assigned ;P New, unrated swappers are allowed, as long as they seem to know what an ATC is. No mentions of ATCs in the profile text will get unrated swappers banned (rated swappers need not worry about that, only their ratings and other questionable behavior).